a) Field of the Invention
The present invention relates to arc lamps, and particularly to mercury arc lamps and metal halide arc lamps; and further particularly to methods for increasing light output, efficiency, and flexibility of use of arc lamps, and for controlling and directing the light of arc lamps.
b) Problems in the Art
Arc lamps represent an efficient, high-intensity source of light, particularly for high intensity, large quantity, or large area lighting. There are many different types of arc lamps, and mercury or metal halide varieties are commonly used for these applications.
Conventional arc lamps are available from a number of manufacturers and generally consist of a mounting apparatus, such as a screw-in or plug-in end, an arc tube, electrical connections connected between the screw-in end and the arc tube, and a bulb surrounding the arc tube, and at least some of the electrical connections.
As can be appreciated, and as is known to those skilled in the art, the arc tube is generally an elongated envelope made of quartz or some other high-temperature resistant yet substantially transparent material. The arc tube has a longitudinal axis which is generally aligned along the longitudinal axis of the entire arc lamp, which in the case of an arc lamp with a threaded end, extends between the threaded end and the opposite end of the lamp.
The arc tube is generally evacuated of air and is loaded with chemicals which facilitate creation of a high-intensity light arc between electrodes which extend into the arc tube, when electricity is applied to the electrodes. The bulb is also evacuated to provide temperature insulation and to provide protection to the arc tube.
In the case of a screw-in arc lamp, the lamp is generally used with a fixture having a threaded socket and a reflector mounted to the socket. The fixture is generally attached to some sort of mounting apparatus for mounting to a supporting structure. The fixture usually must be elevated and adjusted to allow each light to point downwardly to a desired lighting target area, or a desired lighting direction or light aiming path.
A particular problem exists with respect to conventional arc lamps. Because the arc tube is generally aligned along the longitudinal axis of the arc lamp, there is no choice as to orientation of the arc tube once mounted in a fixture. Generally, the lamp and the arc tube are installed in the reflector coaxial with and symmetrical with the primary direction to which the light is directed from the reflector. In other words, the longitudinal axis of the arc tube is coaxial with the longitudinal axis of the arc lamp, which is coaxial with the longitudinal axis of the lamp socket means and reflector means (all defining the aiming direction or axis of the entire lighting fixture). Although this makes sense as far as symmetry and uniformity, it also contributes to a problem called "tilt factor" in mercury and metal halide lamps.
Frequently, the aiming direction of the high power arc lamps will be in an angularly downward orientation. Somewhere below horizontal but not downwardly vertical, the arc lamp and arc tube will therefore also be tilted downwardly with respect to horizontal. Because heat rises, tilting of the arc tube between horizontal and vertical (in any direction), will cause hotter areas to develop at the highest point of the arc tube, generally along the top of the arc tube. In turn, cooler areas will develop at the lowest points, generally along the lower part of the arc tube. These temperature differences, even though the overall temperature through and surrounding the arc tube is quite high, can cause precipitation of some of the loaded chemicals inside the arc tube. Such precipitation will cause clouding and blockage of light, and of course, will also make less of the chemicals available for production of the arc stream, which will also contribute to a reduction in the amount of light possible from the arc lamp. Other detrimental results can be drops in wattage of the lamp of, for example, 3 or 4 percent, and pressure changes in the lamp; all of which can adversely affect the consumption of power by the lamp, making it less efficient and less economical. This problem is thus called the "tilt factor". If a conventional arc lamp is tilted below horizontal, generally between 0.degree. and 45.degree. below horizontal, the tilt factor can result in light output loss of up to 20%.
It can therefore be seen that there is a significant need to solve the tilt factor problem with mercury and metal halide arc lamps. An improvement would represent an increase in efficiency and efficacy (light output, as in lumens per watt).
Another problem with all conventional arc lamps involves the ability to use the light output efficiently and effectively. An arc lamp emits light in such a manner that a majority of the light output radiates radially from the longitudinal axis of the arc tube. Relatively small amounts of light radiate directly from the ends of the arc tube.
Because is always some light loss involved in reflection of light, it is generally most efficient to utilize as much light as possible which comes directly from a light source, as opposed to being reflected. It can therefore be understood that conventional arc lamps which have their arc tubes aligned along the longitudinal axis of both the arc lamp and the aiming axis of the reflector rely significantly on capturing the light emanated radially from the arc tube in the reflector and then redirecting it. If the arc tube did not point directly out of the reflector along its aiming axis, but was offset and/or tilted with respect to that aiming axis, more direct light could be utilized to the target area and reflection loss could be reduced. Also, the beam configuration emanating from the fixture can be made more effective by utilizing the offset and/or tilted arc tube with modifications to the reflector. For example, the reflecting properties of portions of the reflector can be changed to direct more light to the target area. The reflecting properties of the reflector can be altered or added-on features such as visors and shields can be added to the reflector and arc lamp. Inserts can also be added to the reflector. Control and redirection of light within the lighting fixture can be accomplished by using combinations of these types of elements with the offset and/or tilted arc tube. The offset or tilt can be accomplished either by modifying the arc tube in the arc lamp, or by modifying the reflector and fixture in relationship to a conventional non-offset and non-tilted arc tube.
It can therefore be seen that offsetting and/or tilting of the arc tube with respect to the aiming axis of the reflector and/or the target, could result in more direct light, which would eliminate some reflection loss. Offsetting and/or tilting of the arc tube may also have beneficial effects as to allowing a reflector to produce a better beam pattern to the target area. Such an increase in efficiency would deliver more light to the target area. More light could be delivered than with conventional fixtures; or the number of fixtues could be reduced to achieve the same light level.
Furthermore, offsetting and/or angling of the arc tube with respect to the aiming axis of the reflector and with respect to the target area may impact beneficially on glare and/or spill light control. In conventional arc lamps and reflector combinations, a substantial portion of the light is reflected upwardly, or outwardly, outside of the target area. This results many times in glare and spill. By enabling the arc to be offset and/or tilted with respect to the target area and/or the aiming axis of the reflector, it may be possible to eliminate some of the unnecessary spill and glare light, and direct more intensity and usable light to the target area. It may also be possible to more effectively use add-on elements to the reflector or arc lamp. The orientation of the arc tube can thus be utilized in combination with other glare control additions to conventional arc lamp and reflector assemblies to solve significant glare and spill problems, and increase the efficiency of the fixtures with respect to light at the target area.
It is therefore a principle object of the present invention to provide a means and method of increasing light output, efficiency, and flexibility of use of an arc lamp which improves upon or solves the deficiencies and problems in the art.
A further object of the present invention is to provide a means and method as above described, which can be utilized to solve tilt factor problems, light direction problems, and glare and spill problems in arc lamps.
Another object of the present invention is to provide a means and method as above described, which is adaptable to retrofitting of existing lighting fixtures, or is able to be manufactured in desired configurations, or a combination of both.
A further object of the present invention is to provide a means and method as above described, which can be combined with reflector assemblies to increase light, redirect light, and reduce glare and spill problems.
Another object of the present invention is to provide a means and method as above described, which is efficient, and economical to manufacture, install, and maintain.
Another object of the present invention is to provide a means and method as above described which is durable.
These and other objects, features and advantages of the present invention will become more apparent with reference to the accompanying drawings and specification.